As Probability Space opens, the future looks grim, though humanity has spread across the stars. Humans have gained control of a moon-sized, immensely powerful super-weapon abandoned by a long-gone alien race--an artifact that should protect humanity from its implacable enemy, the Fallers, a ruthlessly xenophobic alien race. Unfortunately, the Fallers have found another of these abandoned super-weapons, and if both are discharged at the highest setting at the same time, then the very fabric of space-time will be shredded, destroying not only all life in the universe, but the universe itself. But for the Fallers, victory may be more important than survival. And a violent military coup has put an insanely ambitious general in command of human space....

A novel of literary hard SF, Probability Space concludes the trilogy that begins with Probability Moon and includes Probability Sun. Author Nancy Kress has received the Hugo Award, the Sturgeon Award, and three Nebula Awards.